Studies in both rabbit and murine models of antigen-induced airways hyperresponsiveness suggest enhanced neural release of acetylcholine (ACh) may be responsible for the increased in vitro responsiveness of airway smooth muscle from sensitized animals after antigen challenge. This project has 3 objectives. The first objective is to define the mechanisms responsible for altered neural control of airways after antigen exposure in IgE-sensitized rabbits. The hypothesis that enhanced release of ACh is the primary mechanism responsible for altered neural control will be tested in vitro employing high performance liquid chromatography with electrochemical detection of ACh release in response to electrical field stimulation. In addition, the contribution to this process of substances capable of modulating neural control (platelet activating factor, cyclooxygenase products of arachidonate metabolism, tachykinins) will be addressed. The second objective is to define the effects of antigen exposure on airway epithelial function. The hypothesis that loss or dysfunction of airway epithelial cells contributes to abnormalities in airway control created by IgE-initiated reactions will be tested in rabbits. The time course of epithelial injury and repair after antigen exposure in sensitized and normal rabbits will be defined using antibodies to proliferating cell nuclear antigen, an auxiliary protein of DNA polymerase delta preferentially expressed in the S phase of the cell cycle. Antigen exposure in sensitized rabbits is expected to lead to a significant increase in turnover of airway epithelial cells that parallels the time course of abnormalities in responsiveness created by antigen exposure. The effects of epithelial denudation on neural control mechanisms will be assessed in both normal and sensitized rabbits before and after antigen challenge. The third objective is to define the ability of immunologic stimuli to increase airways responsiveness in inbred strains of mice with different genetic cholinergic sensitivities. The in vitro responsiveness of tracheal smooth muscle from various inbred strains will be defined to both a cholinergic agonist and to electrical field stimulation. Strains most divergent in cholinergic responsiveness will be assessed for anatomic differences in their airways that might explain differences in responsiveness. Strains divergent in cholinergic responsiveness but similar (normal) in airway anatomy will undergo further study. Responsiveness of tracheal smooth muscle from both hyper- and hyporesponsive strains will be assessed before and after sensitization and antigen exposure to address the hypothesis that increases in airways responsiveness will be greater in magnitude and longer in duration in the hyperresponsive strain of mice. The effect of sensitization and challenge on both prejunctional (neural) and postjunctional cholinergic mechanisms will be addressed. Definition of mechanisms that modulate airways responsiveness in normal and sensitized animals subjected to antigen exposure should provide insight into how antigen-initiated IgE responses produce prolonged abnormalities in airways function.